ASHS 2024 Conference

The U.S. Department of Agriculture (USDA) Agriculture Research Service (ARS) has operated a European pear (Pyrus communis) scion breeding program for over a century. The breeding program started in the early 1900s by Merton B. Waite in the Washington D.C. area with the primary objective to develop host resistance to fire blight, a devastating disease caused by Erwinia amylovora. The USDA pear breeding program has continued this effort throughout its history, spanning over six generations of breeders and two cooperative research programs in Michigan and Ohio. The program has released ten named pear varieties, with the first one, 'Waite,' being released in 1938 and the most recent, 'Bell,' in 2022. In this presentation, we discuss the program's history by detailing each generation of breeder(s) aims, their parental selection, and releases. In addition, we present corrected pedigrees for important breeding lines and the releases. Lastly, we present the current objectives of the program, the pedigree complexity of newly generated populations, and the overall success of the program’s primary breeding goal – fire blight resistance.

Interspecific hybrid grapevine cultivars have been developed to expand grape cultivation into cold-climate areas. Cold weather events can lead to bud death and trunk injury which reduce yields and can result in plant death. Phenotyping cold hardiness is challenging, and developing a standardized phenotypic protocol would enable efficient evaluation of University of Minnesota grape breeding germplasm. The objective of this study is to utilize differential thermal analysis as an assay to quantify the low temperature exotherm response of grapevine buds. We phenotyped 28 varieties and advanced breeding selections from October 10th, 2023 through March 20th, 2024. Commercial cultivars (e.g. Marquette, Itasca, Frontenac) and breeding selections (wine grape, table grape, and rootstocks) were sampled weekly or bi-weekly based on availability of plant material. Differences in acclimation and deacclimation patterns between time points were observed in the low temperature exotherm readings, indicating that there may be differences in the genetic mechanisms for cold hardy responses. After the coldest day of the season, January 14, 2024, which had a low of -23°C, the temperature at which 50% of the buds would die, or LT50, for ‘Marquette’, ‘Itasca’, and ‘Frontenac’ were -29.7 °C, -30.9 °C, and -30.5 °C, which is consistent with field observations. The LT50s were rated at lower temperatures than the ambient air temperature, thus all genotypes were able to survive the weather conditions for this cold event. Future analysis aims to utilize K-means cluster analysis to determine groups that differ in responses to winter fluctuations in temperature and to determine the genetic controls for these responses.

The genetic mechanisms controlling fruit morphology in watermelon is not fully understood. Only one candidate gene, ClSUN25-26-27a (Cla011257), has been identified as a significant contributor to the ovary and fruit shape. ClSUN25-26-27a is a member of the SUN gene family, which has been extensively studied in relation to fruit morphology in tomatoes. In tomato, the effect on fruit shape facilitated by this gene is detectable during the early stages of fruit development, with the cell patterns established pre-anthesis. In watermelon, three alleles of ClSUN25-26-27a are known to be associated with ovary and fruit shape variation: the wild-type, a SNP, and a 159bp deletion in the 3rd exon. This study aims to determine the effect of the novel allelic variation for ClSUN25-26-27a on ovary and fruit shape. Four novel alleles have been identified and sequenced in the coding region of ClSUN25-26-27a across three Citrullus species. Marker assisted backcrossing was used to introgress the different alleles into a common genetic background. The NILs were phenotyped in the field to determine the effect of the novel alleles on ovary and fruit shape. Ovary length and width were measured four days pre-enthesis, at anthesis, and four days post-anthesis and used to calculate the ovary shape index (OSI). Mature fruit was also phenotyped using Tomato Analyzer. One of the novel alleles was significantly associated with ovary and fruit shape. These findings contribute to the understanding of the important SUN gene family and the genetic mechanisms contributing to watermelon fruit shape. Future research will determine the gene expression patterns of the different alleles and the effect of the alleles on the cell number or cell size in watermelon.

Mangos are the fifth most consumed fruit in the world (World Atlas). The top five mango producers include India, China, Indonesia, Pakistan, and Mexico (World population). Puerto Rico is the largest U.S. mango producer (2,666 acres), followed by Florida (2,455 acres), Hawaii (497 acres), California (328 acres), and Texas (10 acres). There are thousands of mango cultivars worldwide and the development and selection of new cultivars is ongoing. However, relatively few cultivars have a combination of information on their phenology, metabolomic profiles, consumer preferences, and postharvest handling. Describing and linking these cultivar evaluations and attributes may improve marker-assisted breeding efforts to develop and select for superior mango flavor, aroma, and nutritional value, improve understanding of hedonic consumer preferences, and result in improved postharvest handling and processing of mango. For example, ‘Glenn’ mango is a moderately vigorous tree with an upright open canopy that is generally dormant from November through December-January that flowers during February-March in response to warming ambient temperatures and is harvested during June-July. Historical descriptions are that it is a fruit of excellent eating quality with a rich, aromatic (pineapple notes) flavor, low fiber, and sweet pulp. This is borne out by the nonvolatile physiochemical characteristics of the cultivar including an average TSS of 15.93, TA of 0.65, and TSS/TA ratio of 24.41, with high concentrations of fructose, glucose, isocitric acid, and ketoglutaric acid. Defining nonvolatile flavor constituents from partial least-squares discriminant analysis for ‘Glenn’ mango were fructose, glucose, sucrose, isocitric acid, ketoglutaric acid, malonic acid, and gallic acid whereas defining volatile aroma constituents included ten esters (e.g., ethyl acetate, ethyl butanoate, and ethyl octanoate) that have floral, citrus, sweet, fruity, pineapple, and coconut notes. Results from a consumer sensory (taste, flavor, texture, fibrousness, juiciness, etc.) acceptance study indicated consumers like ‘Glenn’ mango because of its sweetness, tropical flavor, low fiber content, and juiciness, bearing out historical descriptions of this fruit. More detailed metabolic biosynthesis mapping linked flavor precursors and intermediates to the constituents responsible for flavor and aroma of ‘Glenn’. Postharvest evaluations reported ‘Glenn’ was moderately susceptible to hot water treatment injury, significant anthracnose incidence, only slight chilling injury (if stored below the 13°C recommended temperature) and could be stored for at least 3 weeks.

Since the 1920’s, Oregon State University (OSU) and the United States Department of Agriculture (USDA) Horticultural Crops Production and Genetic Improvement Research Unit have cooperated in the public breeding and development of small fruit cultivars to support Pacific Northwest (PNW) production. Together, the PNW states of Oregon and Washington have significant berry production with 152,407 metric tons of blueberry (Vaccinium spp.), 24,494 metric tons of red and black raspberry (Rubus idaeus; R. occidentalis), 9,525 metric tons of blackberry (Rubus spp.), and 6,804 metric tons of strawberry (Fragaria x ananassa) in 2022. Processed berries are the primary regional market, with fresh market production a lesser but still important driver for small farms. To continue to improve regional production of high-quality fruit, cultivar development has been a top tier research priority for PNW berry commodity commissions over the past decade. The cooperative breeding program has a continual germplasm improvement cycle that includes plant material in all stages of development, from seedlings, observational and replicated field trials, grower trials, and cultivar releases. After seedling evaluation, promising advanced selections of strawberry, blueberry, blackberry, red raspberry, and black raspberry crops are assessed at the OSU North Willamette Research and Extension Center in Aurora, Oregon. The USDA and OSU cooperative breeding program, in collaboration with Washington State University, has a uniquely strong focus on developing machine harvestable small fruit cultivars. Over 20 cultivars have been released with a value to PNW industries of over $450 million in the last ten years. ‘Tillamook’ strawberry, and ‘Black Diamond’ and ‘Columbia Star’ blackberry lead the acreage in Oregon and were developed by the program. More than 50 berry cultivars have been released since 1942 exclusively by the USDA with another 16 jointly-released with other agricultural universities and international corporations. This presentation will outline the cooperative breeding framework, discuss breeding priorities, and highlight new and upcoming cultivar releases.

Hybrid grapevines (Vitis spp.) grown in cold climate regions have fruit chemistries which do not adhere to the standard ranges of European wine grapes (Vitis vinifera L.) that many consumers may be accustomed to. The variation in fruit chemistry observed in hybrid grapevines is driven by a combination of genetics of parent material, which often builds on wild Vitis species, and the environmental conditions of production, which are often characterized by low heat accumulation and limited duration of growing season. Characterizing the genetic basis of fruit attributes enables breeders to understand and improve the relative quality of interspecific grapevines for future cultivar development. To address this knowledge gap for breeders, an incomplete diallel population of interspecific hybrid grapevines was assessed over a period of three years. Fruit chemistry (total soluble solids, pH, total acidity, glucose, fructose, malic acid, tartaric acid, citric acid, and yeast assimilable nitrogen content) and berry mass were examined at three distinct time points within each growing season to yield a total of nine phenotyping events. Best linear unbiased predictors (BLUPs) calculated from multi-year phenotype data were then interrogated via GWAS analysis to identify significant marker-trait associations. Chromosomes 16, 6, and 17 were noted to have the highest number of associations observed. To further understand the specificity of observed loci, gene annotation was conducted to reveal several important genes potentially related to the phenotypes. Due to the quantitative nature of fruit attributes, genomic selection strategies were explored to assess their accuracy for improving population performance in a systematic manner. Cumulatively, this analysis provides important information regarding the role of genetics in major fruit traits of interspecific cold hardy grapevines, regions of interest for fine mapping, and strategies for genomic selection. These analyses contribute towards the goals of improving breeding efficiency and selection accuracy to reduce generation timeline in grapevines.

Peach is an introduced crop with a relatively short production and breeding history in the U.S. The peach industries have been facing declines and challenges in both production and breeding activities over the past decades. Understanding of the statuses and issues facilitates gaining insights and finding solutions. This presentation is to provide an overview of U.S. peach production and breeding, including trends, issues, and prospects. Both U.S. peach acreage and production are declining, but market values increasing. Public peach breeding programs were established at the early time and helped establish considerable production in many states. But most of them have been terminated, phased out, or de-emphasized, largely due to declining production and economic impact. Taken into consideration all factors, visionary peach horticulture research and breeding solutions for some cost-related and yield-limiting production issues are essential for profitable and sustainable peach production in the future.

The University of Arkansas System Division of Agriculture (UADA) has a legacy breeding program that has spanned three fruit breeders and 60 years. The UADA Fruit Breeding Program is large, complex, and works on multiple crops. A recent program initiative has been the introduction of modern tools for breeding approaches and data collection and management. This talk will outline the process for developing a molecular breeding pipeline for blackberry (Rubus subgenus Rubus Watson) and muscadine grape (Muscadinia rotundifolia) and outline how these approaches benefit program progress. Additionally, advances in data collection techniques such as digital evaluations using an application and development of barcoding systems for streamlining processes and minimizing error will be described.